Two electrode spark gap apparatus

ABSTRACT

A hermetically sealed spark gap discharge device of the type wherein the spacing between two electrodes can be set after the electrodes have been mounted within the enclosure. The spark gap apparatus can be completely assembled except for the hermetically sealing of the spark gap apparatus and the setting of the spacing between the two electrodes that establishes the arc discharge when a predetermined breakdown voltage is established across the electrodes.

United States Patent 1 1 Kozlowski Se t. 16 1975 [54] TWO ELECTRODE SPARK GAP 3,513,516 5/1970 Oddo et a1. 313/146 X APPARATUS 3,562,574 2/1971 w6SO10Sk1 313/178 X Y [75] Inventor: Joseph M. Kozlowski, Sidney, NY. Primary Examiner R. V. Rolinec [73] Assignee: The Bendix Corporation, Southfield, Assistant in R. H stetter Mi h I Attorney, Agent, or FirmRaymond J. Eifler [22] Filed: Jan. 16, 1974 ABSTRACT [21] App!" 433943 A hermetically sealed spark gap discharge device of r the type wherein the spacing between two electrodes 52 us. (:1. 313/220; 313/146; 313/221; can be Set after the electrodes have been mounted 313/217 within the enclosure. The spark gap apparatus can be 511 Int. Cl. H01 j 17/16 eempleteiy assembled except for the hermetically Seal- [58] Field of Search 313/146, 217, 220 g of the Spark p apparatus and the Setting of the spacing between the two electrodes that establishes 5 References Cited the arc discharge when a predetermined breakdown UNITED STATES PATENTS voltage is established across the electrodes.

3.363.134 H1968 Johnson 313/220 8 Claims, 5 Drawing Figures TWO ELECTRODE SPARK GAP APPARATUS BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for controlling the discharge of electrical energy. The invention is more particularly related to a spark gap discharge device.

Gaseous conductors such as spark gap discharge devices have numerous applications. Generally, a spark gap discharge apparatus is used as a trigger to isolate energy stored in a capacitor from a load. One example of such a use is in blasting operations in tunnels and shaft mining where it is desirable to detonate explosives with electric blasting caps. Typically, the electric blasting caps are detonated by electric energy which is received from the discharge of a storage capacitor. Obviously, the most important aspects of blasting is the safety of the people involved in the operations. Therefore, a most important feature of any blasting circuit is the device that isolates the explosives from the electrical energy that detonates the explosives. A description of one such device may be found in US. Pat. No. 3,715,614 entitled Three Electrode Spark Gap Apparatus issued Feb. 6, 1973 to Irving E. Linkroum.

' Another use for spark gap discharge devices is in the ignition circuitry for industrial and aircraft gas turbine engines wherein the spark gap device is used to isolate and trigger the discharge of the energy stored in a capacitor into an igniter plug that ignites fuel in the engine.

' Within the aforementioned applications, it is generally necessary that the spark gap apparatus have a specific breakdown voltage at which the spark gap apparatus will allow the discharge of energy into the load, e.g. igniter plug or blasting caps. Further, it is necessary that there be a wide variety of spark gap devices, each having a predetermined breakdown voltage that corresponds to the circuitry for which it is to be used. This requirement has in the past necessitated the need for stocking a large number of spark gap devices with different electrode spacings.

SUMMARY OF THE INVENTION This invention eliminates the need to stock spark gaps with different electrode spacings by providing a completely assembled spark gap electrode assembly that includes an electrode that is adjustable to establish the desired breakdown before the apparatus is hermetically sealed.

The invention is a spark gap apparatus (See FIG. for a capacitor discharge circuit that is characterized by the additional element of a flanged sleeve 3 that allows one of the electrodes 20 to be adjusted before the apparatus is hermetically sealed.

In one embodiment of the invention, the spark gap apparatus comprises: a tube 5 having a central axis; a first base I mounted at one end of the tube; a second base 2 mounted at the other end of the tube and forming with the first base 1 and the tube 5 an enclosure; a first electrode mounted to the first base 1 and extending into the enclosure along the central axis thereof, the first electrode I0 having a free end portion that includes an arc discharge surface area 11; a flanged sleeve 3 mounted to and extending through the second base 2 in the manner shown in FIGS. 3 and 5; and a second electrode mounted through the sleeve 3 and extending into the enclosure along the central axis, the second electrode 20 having a free end portion that includes an arc discharge surface 21 which is spaced from and faces the arc discharge surface 11 of the first electrode 10, the second electrode 20 electrically isolated from the first electrode; and means for hermetically sealing the enclosure formed by the first and second bases 10,20 and the tube 5.

Accordingly, it is an object of this invention to provide a spark gap apparatus that has an adjustable electrode.

Another object of this invention is to provide an improved device for discharging capacitors.

It is still another object of this invention to provide an apparatus that allows the electrode spacing therein to be established after the device is assembled but before the device is hermetically sealed.

It is still another object of this invention to provide spark discharge devices, having different breakdown voltage, which are made from the same preassembled device.

The above and other objects and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings and claims which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross-sectional view of a spark gap discharge apparatus that incorporates the principles of the invention.

FIG. 2 is a cross-sectional view of the apparatus shown in FIG. 1 taken along lines IIII.

FIG. 3 is a plan view of the spark gap discharge apparatus shown in FIG. 1.

FIG. 4 is an end view of the spark gap discharge apparatus shown in FIG. 3.

FIG. 5 is a partial cross-sectional view of one end portion of a spark gap discharge apparatus.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now to the drawings, FIG. 1 illustrates a spark gap discharge device that is useful for triggering the energy stored in a capacitor discharge circuit. The spark gap device shown may be used in blasting machine circuits as serve as a switch for discharging the energy stored in the capacitor through blasting caps to detonate dynamite. The device illustrated has been found to be greatly superior to mechanical switches in this application because the contacts of mechanical switches burn away after relatively few operations because of the energy passing through them. Ordinary gaseous conductors are inappropriate for use in discharging the energy from a storage capacitor when the energy stored in the capacitor is greater than joules.

FIG. 1 illustrates a spark gap discharge apparatus which comprises: an enclosure formed by base plates 1 and 2 which are mounted to the ends of a tube 5; and electrodes 10 and 20 mounted to the base plates 1 and 2 respectively along the central or longitudinal axis of the tube 5. The base plates 1 and 2, tubing 5 and tubing 10 and 3 are selected from materials having approximately the same thermal coefficient of expansion 5 X l() 1C in the expected operating temperature range (65F to 5()()F). The base plates 1 and 2 are comprised of a borosilicate glass (Corning 7052); the tubing 5 is comprised of a ceramic such as alumina (96% A1 and the metal parts such as tubes 3 and 10, and washer 31 are comprised of an ASTM F15 alloy (c.g. Kovar, Rodar, Nicoseal). When the assembled parts are properly fixtured and exposed to an appropriate temperature, the glass will melt and bond to the adjacent surfaces to form an air-tight enclosure upon cooling. The enclosure may be evacuated through the passage 15 and hole 16 in the electrode tubing 10. The enclosure may be evacuated to a pressure below 1 X 10 torr and then backfilled with an ionizable atmosphere to a pressure at, above or below atmospheric. Repeated evacuationand backfilling will flush out undesirable gases. Preferred ionizable atmospheres that may be used to backfill the enclosure are dry air or a mixture of dry air or a mixture of argon and hydrogen. Other gas mixtures such as: air and carbon dioxide, nitrogen, hydrogen and argon may also be used. Alternately tubing 5 may be comprised of a suitable glass and the enclosure may be evacuated through a tubulation in the glass.

The arc discharge surfaces 11, 21 of the electrodes and 20 are comprised of materials chosen for their electrical and physical characteristics at high currents, voltages and temperatures. Examples of acceptable electrode materials are molybbenum, tungsten, thoriated tungsten, and tungsten mixed with metals such as thorium,' aluminum, and barium to provide a lower work function than tungsten. Because of the high energy associated with the discharge across the electrodes, tungsten is an electrode material that is suitable for the anode and cathode because of its high temperature characteristics (high melting temperature). Barium aluminate may be added to the tungsten to improve the electrical characteristics of those of the electrodes as barium aluminate increases the emissivity of electrodes. For a detailed discussion of gaseous conductors see Vacuum Tube and Semiconductor Electronics", and Gaseous Conductors by James Cobine published by Dover Publications.

The first electrode 10, mounted to the first base 1, extends into the enclosure and terminates at a free end that includes an arc discharge surface 11. The first electrode 10 includes an axial passage that includes an. opening 16. In this embodiment, the first electrode 10 serves as the conduit for evacuating the enclosure and filling it with an ionizable atmosphere. The second electrode is mounted through the second base 2, ex tends into the enclosure and terminates in an are discharge surface 21. The second base 2 extends along the central axis of the enclosure through sleeve 3 that receives the electrode 20. The sleeve 3 maintains the electrode 20 substantially along the central axis of the enclosure and in alignment with the axis of the other electrode 10, while permitting axial movement of the electrode 20 with respect to the electrode 10. The sleeve 3 is positioned by inner plate 31 which prevents the sleeve 3 and base 2 from falling into the enclosure during the assembly procedure. The movable electrode 20 permits the spacing, between the arc discharge surfaces ll, 21 between the electrodes 10 and 20, to be accomplished after the enclosure is fabricated but before the enclosure is filled with an ionizable atmosphere and the enclosure hermetically sealed.

FIG. 2 is a cross-sectional viewof the spark gap discharge device shown in FIG. 1 taken along lines 11-".

This figure illustrates the generally cylindrical shape of the tubing 5 and how the electrode 10 is mounted along the central axis of the tubing 5.

FIG. 3 illustrates a spark gap discharge device that is completely assembled and ready for operation. The device shown in FIG. 3 has been hermetically sealed and the spacing between the discharge surfaces 11, 21 of the electrodes 10 and 20 has been fixed. The spacing between the electrodes 10 and 20 has been fixed by crimping tube 3 at point 32 to the electrode 20 to prevent movement of electrode 20. The tube 3 and electrode 20 are then hermetically-sealed by soldering or silveralloy brazing 33. Similarly, after the spark gap discharge device has been filled with an ionizable atmosphere, electrode 10 is then crimped at 12 and soldered or silver-alloy brazed at the end 13 to produce a hermetically sealed joint.

FIG. 4 is an end view of the spark gap discharge apparatus shown in FIG. 3 which illustrates that electrode 10 is arranged along the central axis of the tube 5.

FIG. 5 is an alternate embodiment of one end portion of a spark gap discharge device shown in FIG. 1. In this embodiment, the sleeve 3 is made integral with plate 31 and extends from one end of the device from below the base 2. To hermetically seal the sleeve portion 3 to the tube 5, a glass washer 2, preferably comprised of a borosilicate, is placed over the metal tubing 3 and plate 31 and sealed to the conduit 3 and tubing 5 by raising the temperature of the glass until it melts and forms a hermetic seal.

A preferred method of fabrication would be accomplished as follows: All of the components of a spark gap discharge apparatus are fabricated into the assembly shown in FIG. 1. The glass bases 1 and 2, are heated to a high temperature to melt the glass and establish a seal between the tube 5 and the bases 1 and 2 and electrode 10 and sleeve 3. The assembly is then stored until a requirement comes for a spark gap discharge device having a particular breakdown voltage. Upon receipt of a request for spark gap discharge devices each having various breakdown voltages, the devices are assembled into operational device as follows: First, the enclosure is purged of any undesirable gases and moisture by a flushing with either dry air or argon. The gap spacing is then adjusted by axially moving electrode 20 into contact with electrode 10 and then axially backing off electrode 20 to the desired spacing between the discharge surfaces 11 and 21. Once the desired spacing is established, it may be checked by attaching an electrical instrument to the electrodes that establishes a voltage below the breakdown potential required. The voltage is then increased until there is a breakdown of the potential between the two electrodes. This breakdown should correspond to the breakdown voltage desired by setting the gap. If it does not, the electrode 20 may be moved closer or further away from electrode 10 depending on the voltage at which the breakdown occurs. Once the proper voltage breakdown is obtained by properly spacing the electrodes, electrode 20 is made immovable by crimping the sleeve 3 to the electrode 20. Next, the sleeve 3 is soldered or silver-alloy brazed to the electrode 20 to seal this end of the enclosure. The only remaining opening to the inside of the enclosure is through the passage 15 in electrode 10 that terminates in opening 16 within the enclosure. The final step in making the tubeopera'tional is to fill the enclosure with a; predetermined gas and to a predetermined pressure or vacuum level. The final step is sealing off the passage by crimping one end of the electrode 10 and soldering or silver-alloy brazing the walls of the electrode 10 together to produce a sealed joint. The final result is a hermetically sealed spark electrode discharge apparatus.

In operation, the spark gap discharge device will operate as follows: When the voltage across the spark gap discharge device reaches the breakdown potential, an electric arc is initiated between electrodes 10 and 20. The value of the voltage breakdown necessary to initiate the discharge is a function of the voltage between the electrodes, the electrode materials, the spacing between the electrodes, the gas in the enclosure, and the pressure of the gas within the enclosure. Once an arc is established between the electrodes 10 and 20, energy stored in a storage capacitor, in electrical circuit relationship with the spark gap apparatus, begins to discharge through the arc and into the load.

While a preferred embodiment of the invention has been disclosed, it will be apparent to those skilled in the art that changes may be made to the invention as set forth in the appended claims, and in some cases, certain features of the invention may be used to advantage without corresponding use of other features. For example, the electrodes and enclosure may take shapes other than cylindrical. Accordingly, it is intended that the illustrative and descriptive materials herein be used to illustrate the principles of the invention and not to limit the scope thereof.

Having described the invention, what is claimed is:

1. A spark gap apparatus comprising:

a ceramic tube having a central axis;

a first base mounted at one end of said tube;

a second base comprised of glass mounted at the other end of said tube and forming with said first base and said tube an enclosure;

a first electrode mounted to said first base and extending into said enclosure along said central axis, said first electrode having a free end portion that includes an arc discharge surface;

a metal plate disposed inside of and transverse to the central axis of said tube, said metal plate being in contact with an annular portion of said second base and an annular portion of said tube;

a sleeve mounted to and extending through said second base; and

a second electrode mounted through said sleeve and said metal plate and extending into said enclosure along said central axis, said second electrode having a free end portion that includes an arc discharge surface which is spaced from and faces the arc discharge surface of said first electrode, said second electrode electrically isolated from said first electrode.

2. The spark gap apparatus recited in claim 1 including:

means for hermetically sealing the enclosure formed by said bases and said tube.

3. The spark gap apparatus described in claim 1 wherein said first electrode has a passage therein along said central axis, one end of said first electrode passage terminating outside of said enclosure and an opening in another portion of said electrode that communicates with said first electrode passage and the inside of said enclosure.

4. The spark gap apparatus recited in claim 1 wherein said enclosure contains an ionizable atmosphere.

5. The spark gap apparatus recited in claim 3 wherein said enclosure contains an ionizable atmosphere.

6. The spark gap apparatus claimed in claim 1 wherein said ceramic material is alumina.

7. The spark gap apparatus claimed in claim 5 wherein said ceramic material is alumina.

8. The spark gap apparatus described in claim 2 wherein said first electrode has a passage therein along said central axis, one end of said first electrode passage terminating outside of said enclosure and an opening in another portion of said electrode that communicates with said first electrode passage and the inside of said enclosure. 

1. A spark gap apparatus comprising: a ceramic tube having a central axis; a first base mounted at one end of said tube; a second base comprised of glass mounted at the other end of said tube and forming with said first base and said tube an enclosure; a first electrode mounted to said first base and extending into said enclosure along said central axis, said first electrode having a free end portion that includes an arc discharge surface; a metal plate disposed inside of and transverse to the central axis of said tube, said metal plate being in contact with an annular portion of said second base and an annular portion of said tube; a sleeve mounted to and extending through said second base; and a second electrode mounted through said sleeve and said metal plate and extending into said enclosure along said central axis, said second electrode having a free end portion that includes an arc discharge surface which is spaced from and faces the arc discharge surface of said first electrode, said second electrode electrically isolated from said first electrode.
 2. The spark gap apparatus recited in claim 1 including: means for hermetically sealing the enclosure formed by said bases and said tube.
 3. The spark gap apparatus described in claim 1 wherein said first electrode has a passage therein along said central axis, one end of said first electrode passage terminating outside of said enclosure and an opening in another portion of said electrode that communicates with said first electrode passage and the inside of said enclosure.
 4. The spark gap apparatus recited in claim 1 wherein said enclosure contains an ionizable atmosphere.
 5. The spark gap apparatus recited in claim 3 wherein said enclosure contains an ionizable atmosphere.
 6. The spark gap apparatus claimed in claim 1 wherein said ceramic material is alumina.
 7. The spark gap apparatus claimed in claim 5 wherein said ceramic material is alumina.
 8. The spark gap apparatus described in claim 2 wherein said first electrode has a passage therein along said central axis, one end of said first electrode passage terminating outside of said enclosure and an opening in another portion of said electrode that communicates with said first electrode passage and the inside of said enclosure. 